Natures wonders: giraffe circulatory system (Introduction)

by David Turell @, Monday, June 27, 2016, 00:08 (1383 days ago) @ David Turell

There is no way the circulatory controls for the giraffe's circulation could have developed bit by bit. The long neck requires blood pressure regulation when the head is high and very different when the animal drinks:

"The advantage of the giraffe's long neck for "browsing on the higher branches of trees" is, however, not nearly as obvious as Darwin makes out. Consider that the neck of the female giraffe is two feet shorter, on average, than that of the male. If a longer neck were needed solely to reach above the existing forage line, then the females would have soon starved to death and the giraffe would have become extinct.


"When a giraffe stands in its normal upright posture, the blood pressure in the neck arteries will be highest at the base of the neck and lowest in the head. The blood pressure generated by the heart must be extremely high to pump blood to the head. This, in turn, requires a very strong heart. But when the giraffe bends its head to the ground it encounters a potentially dangerous situation. By lowering its head between its front legs, it puts a great strain on the blood vessels of the neck and head. The blood pressure together with the weight of the blood in the neck could produce so much pressure in the head that, without safeguards, the blood vessels would burst.

"Such safeguards, however, are in place. The giraffe's adaptational package includes a coordinated system of blood pressure control. Pressure sensors along the neck's arteries monitor the blood pressure and can signal activation of other mechanisms to counter any increase in pressure as the giraffe drinks or grazes. Contraction of the artery walls, the ability to shunt arterial blood flow bypassing the brain, and a web of small blood vessels between the arteries and the brain (the rete mirabile, or "marvelous net") all control the blood pressure in the giraffe's head. The giraffe's adaptations do not occur in isolation but presuppose other adaptations that all must be carefully coordinated into a single, highly specialized organism.

"In short, the giraffe represents not a mere collection of isolated traits but a package of interrelated traits. It exhibits a top-down design that integrates all its parts into a single functional system. How did such an adaptational package arise? According to neo-Darwinian theory, the giraffe evolved to its present form by the accumulation of individual, random genetic changes that were sifted and preserved piecemeal by natural selection. But how could such a piecemeal process, in which mutation and selection act on the spur of the moment with no view to the future benefit of the organism, bring about an adaptational package, especially when the parts that make up the package are useless, or even detrimental, until the whole package is in place? That's the trouble with integrated packages -- they are package deals that offer no benefit until the entire package is in place.


"Major changes, such as the evolution of a giraffe from an animal with short legs and short neck, would require an extensive suite of coordinated adaptations. The complex circulatory system of the giraffe must appear at the same time as its long neck or the animal will not survive. If the various elements of the circulatory system appear before the long neck, they are useless or even detrimental. This interdependence of structures strongly suggests a top-down design that is capable of anticipating the total engineering requirements of organisms like the giraffe.


"The Cambrian explosion marks the sudden appearance in the fossil record of numerous multicellular animals exhibiting diverse body plans. For most of these animals, evidence of fossil ancestors is completely lacking (with but one or two exceptions, there are no known Precambrian precursors). And yet these organisms arrive fully formed in the fossil record as integrated adaptational packages.


"There is no evidence of mutations in fruit flies creating new structures. Mutations merely alter existing structures. For instance, mutations have produced crumpled, oversized, and undersized wings. They have produced double sets of wings (one set of which doesn't work and thus is deleterious to the organism). But they have not created a new kind of wing. Mutations have also created monstrosities, like fruit flies with legs growing where they should have antennae (a condition known as Antennapedia). But even such monstrosities merely rearrange existing structures, albeit in bizarre ways. Nor have mutations transformed the fruit fly into a new kind of insect. Experiments have simply produced variations of fruit flies.


"In conclusion, to generate an adaptational package requires not piecemeal change but integrated, systematic change. Moreover, the source of such change must impart massive amounts of new functional information into an organism. Such information, however, gives no evidence of resulting from the interplay of mutation and selection. Indeed, it gives no evidence of being reducible to matter and energy at all."

Comment: These changes are saltations, not available by Darwin's thoughts. The fruit fly mutation experiments show that. God, anyone?

Complete thread:

 RSS Feed of thread

powered by my little forum